Polymorphism denotes the existence of more than one crystal structure of a chemical entity. For any specific chemical entity it is not readily predictable that it will exhibit polymorphism. In the instance when the chemical entity is a drug, the ability of the chemical entity to exist in more than one crystal form can have a profound effect on the shelf life, solubility, formulation properties, and/or processing properties of the drug. Furthermore, the biological action of the drug can be affected by the polymorphism. Different crystalline forms can possess varying rates of uptake in the body, leading to lower or higher biological activity than required. An undesired polymorph may even show toxicity. Therefore the occurrence of an unknown polymorphic form during manufacture and processing of a drug can have a profound impact.
It is therefore important to be able to understand and control polymorphism. Predicting any possible polymorphs for a drug can diminish the possibility of contamination during a drug's manufacture or storage by other polymorphic forms.
Also, understanding which crystal structures are possible in some cases allows researchers to maximize the desired properties of a compound, such as solubility, formulation properties, processing properties, and shelf life. Understanding these factors early in the development of a new drug may mean a more active, more stable, or more cheaply manufactured drug.